Liquid crystal display device

ABSTRACT

A liquid crystal display device according to FFS technology is capable of providing a common electrode with common electric potential. A pixel electrode is formed of a first layer transparent electrode. A common electrode made of a second layer transparent electrode is formed above the pixel electrode interposing an insulation film between them. The common electrode in an upper layer is provided with a plurality of slits. The common electrode extends over all the pixels in a display region. An end of the common electrode is disposed on a periphery of the display region and connected with a peripheral common electric potential line that provides a common electric potential Vcom. There is provided neither an auxiliary common electrode line nor a pad electrode, both of which are provided in a liquid crystal display device according to a conventional art.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 11/878,579, filed Jul. 25, 2007, which applicationclaims priority to Japanese Priority Patent Application JP 2006-204624filed in the Japan Patent Office on Jul. 27, 2006, the entire content ofwhich is hereby incorporated by reference.

BACKGROUND

This invention relates to a liquid crystal display device, specificallyto a liquid crystal display device in which an alignment direction ofliquid crystal molecules is controlled by a lateral electric fieldgenerated between a pixel electrode and a common electrode.

As a way to achieve a wide viewing angle of the liquid crystal displaydevice, a method has been developed to realize a light switchingfunction by rotating the liquid crystal molecules in a plane parallel toa substrate with a lateral electric field generated between theelectrodes on the same substrate. In-Plane Switching (hereafter referredto as IPS) technology and Fringe-Field Switching (hereafter referred toas FFS) technology, which is an improved IPS technology, are known asexamples of these technologies.

A manufacturing process of the liquid crystal display device accordingto the FFS technology will be explained referring to the drawings. FIGS.18A through 20B show the manufacturing process of one pixel in theliquid crystal display device according to the FFS technology. FIGS.18A, 19A and 20A are plan views of a part of a display region in theliquid crystal display device. Each of FIGS. 18B, 19B and 20B is across-sectional view showing a section A-A in each of FIGS. 18A, 19A and20A, respectively. Although a large number of pixels are disposed in amatrix form in the display region in the actual liquid crystal displaydevice, only three pixels are shown in each of the plan views.

A buffer layer 11, which is made of a silicon dioxide (SiO₂) film or asilicon nitride (SiNx) film, and an amorphous silicon layer aresuccessively formed by CVD (Chemical Vapor Deposition) on a TFTsubstrate 10, which is made of a glass substrate or the like, as shownin FIG. 18B. The amorphous silicon layer is crystallized and transformedinto a polysilicon layer by excimer laser annealing. The polysiliconlayer is patterned to form a U-shaped active layer 12 of a thin filmtransistor 1 (hereafter referred to as TFT 1).

After that, a gate insulation film 13 is formed to cover the activelayer 12. A gate line 14 made of chromium, molybdenum or the like isformed on the gate insulation film 13 overlapping the active layer 12.The gate line 14 extends in a row direction, and intersects the activelayer 12 at two locations. A gate signal that controls turning on/off ofthe TFT 1 is applied to the gate line 14. On the other hand, anauxiliary common electrode line 15, that is made of the same material asthe gate line 14 and is for providing a common electric potential Vcom,is formed parallel to the gate line 14.

Next, there is formed an interlayer insulation film 16 that covers theTFT 1 and the auxiliary common electrode line 15. And contact holes CH1and CH2, which expose a source region 12 s and a drain region 12 d inthe active layer 12, respectively, are formed in the interlayerinsulation film 16. Also, a contact hole CH3, that exposes the auxiliarycommon electrode line 15, is formed in the interlayer insulation film16.

There are formed a source electrode 17 that is connected with the sourceregion 12 s through the contact hole CH1, a display signal line 18 thatis connected with the drain region 12 d through the contact hole CH2,and a pad electrode 19 that is connected with the auxiliary commonelectrode line 15 through the contact hole CH3. The source electrode 17,the display signal line 18 and the pad electrode 19 are made of metalincluding aluminum or aluminum alloy or the like. Next, a planarizationfilm 20 is formed over the entire surface. Contact holes CH4 and CH5,that expose the source electrode 17 and the pad electrode 19respectively, are formed in the planarization film 20.

And there is formed a pixel electrode 21 that is connected with thesource electrode 17 through the contact hole CH4 and extends over theplanarization film 20, as shown in FIGS. 19A and 19B. The pixelelectrode 21 is made of a first layer transparent electrode such as ITO(Indium Tin Oxide), and is applied a display signal Vsig from thedisplay signal line 18 through the TFT 1.

After that, an insulation film 22 is formed to cover the pixel electrode21, as shown in FIG. 20B. A contact hole CH6, that exposes the padelectrode 19, is formed by etching the insulation film 22. A commonelectrode 23, that has a plurality of slits S, is formed on the pixelelectrode 21 through the insulation film 22. The common electrode 23 ismade of a second layer transparent electrode such as ITO, and isconnected with the pad electrode 19 through the contact hole CH6.

A counter substrate 30 made of a glass substrate or the like is disposedfacing the TFT substrate 10. A polarizing plate 31 is attached to thecounter substrate 30. Also, a polarizing plate 32 is attached to a backsurface of the TFT substrate 10. The polarizing plates 31 and 32 aredisposed in a way that their polarization axes are perpendicular to eachother. A liquid crystal 40 is sealed-in between the TFT substrate 10 andthe counter substrate 30.

In the liquid crystal display device described above, an averagealignment direction (hereafter simply referred to as “alignmentdirection”) of major axes of the liquid crystal molecules of the liquidcrystal 40 is parallel to the polarization axis of the polarizing plate32 when a display voltage is not applied to the pixel electrode 21 (novoltage state). In this case, linearly polarized light passing throughthe liquid crystal 40 does not go through the polarizing plate 31because its polarization axis is perpendicular to the polarization axisof the polarizing plate 31. That is, black is displayed.

When the display voltage is applied to the pixel electrode 21, on theother hand, there is generated a lateral electric field from the pixelelectrode 21 toward the common electrode 23 through the slits S. Theelectric field is perpendicular to a longitudinal direction of the slitsS on the plan view, and the liquid crystal molecules are rotated along aline of electric force of the electric field. At that time, the linearlypolarized incident light to the liquid crystal 40 is turned intoelliptically polarized light by birefringence to have a component oflinearly polarized light that passes through the polarizing plate 31. Inthis case, white is displayed. The liquid crystal display deviceaccording to the FFS technology is disclosed in Japanese PatentApplication Publication Nos. 2001-183685 and 2002-296611.

In general, when the common electrode 23 is insufficiently provided withthe common electric potential Vcom because of an influence of electricresistance, the voltage applied to the liquid crystal 40 is reduced tocause degradation in quality of display such as reduced contrast. Sincethe common electrode 23 is formed of the transparent electrode such asITO that has higher sheet resistivity than ordinary metal, thedegradation in the quality of display is prone to be caused. Thisproblem becomes evident particularly as a panel size of the liquidcrystal display device becomes larger. Therefore, in order to providethe common electrode 23 with the common electric potential Vcomsufficiently, the auxiliary common electrode line 15 that supplies thecommon electric potential Vcom is disposed within the display region andthe auxiliary common electrode line 15 is connected with the commonelectrode 23 in each of the pixels in the conventional liquid crystaldisplay device.

When the auxiliary common electrode line 15 is disposed within thedisplay region, however, there is a problem that its wiring portionmakes a light-shielding region to reduce an aperture ratio of thepixels. This invention is directed to offer a liquid crystal displaydevice capable of securely providing the common electrode with thecommon electric potential sufficiently and improving the aperture ratioof the pixels to obtain a bright display.

SUMMARY

A liquid crystal display device of this invention includes a substrate;a plurality of pixels disposed in a display region on the substrate,each of the pixels including a pixel electrode and a common electrodehaving a plurality of slits and disposed on the pixel electrode throughan insulation film and extending over the plurality of the pixels; and aperipheral common electric potential line provided with a commonelectric potential and disposed on a periphery of the display region,wherein an end of the common electrode is connected with the peripheralcommon electric potential line.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view showing a portion of a display region in a liquidcrystal display device according to a first embodiment of thisinvention.

FIG. 2 is a cross-sectional view showing a section X1-X1 in FIG. 1.

FIG. 3 shows a first layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 4 shows a second layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 5 shows a third layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 6 shows a fourth layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 7 shows a fifth layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 8 shows a sixth layout of the liquid crystal display deviceaccording to the first embodiment of this invention.

FIG. 9 is a plan view showing a portion of a display region in a liquidcrystal display device according to a second embodiment of thisinvention.

FIG. 10 is a cross-sectional view showing a section X2-X2 in FIG. 9.

FIG. 11 is a cross-sectional view showing a section Y1-Y1 in FIG. 9.

FIG. 12 is a plan view showing a portion of a display region in a liquidcrystal display device according to a third embodiment of thisinvention.

FIG. 13 is a cross-sectional view showing a section X3-X3 in FIG. 12.

FIG. 14 is a cross-sectional view showing a section Y2-Y2 in FIG. 12.

FIG. 15 is a plan view showing a portion of a display region in a liquidcrystal display device according to a fourth embodiment of thisinvention.

FIG. 16 is a cross-sectional view showing a section X4-X4 in FIG. 15.

FIG. 17 is a cross-sectional view showing a section Y3-Y3 in FIG. 15.

FIGS. 18A and 18B are for explanation of a structure and a manufacturingmethod of a liquid crystal display device according to a conventionalart.

FIGS. 19A and 19B are for explanation of the structure and themanufacturing method of the liquid crystal display device according tothe conventional art.

FIGS. 20A and 20B are for explanation of the structure and themanufacturing method of the liquid crystal display device according tothe conventional art.

DETAILED DESCRIPTION

Embodiments of the present application will be described below in detailwith reference to the drawings.

A liquid crystal display device according to a first embodiment of thisinvention will be explained referring to the drawings. FIG. 1 is a planview showing a portion of a display region in the liquid crystal displaydevice. FIG. 2 is a cross-sectional view showing a section X1-X1 inFIG. 1. Although a large number of pixels are disposed in a matrix formin the display region 70 in the actual liquid crystal display device,only three pixels are shown in the plan view.

A pixel electrode 21 is formed of a first layer transparent electrode. Acommon electrode 23A made of a second layer transparent electrode isformed above the pixel electrode 21 interposing an insulation film 22between them. The common electrode 23A in an upper layer is providedwith a plurality of slits S. The structures described above aregenerally common to the structure shown in FIGS. 20A and 20B. In theembodiment, however, the common electrode 23A extends over all thepixels in the display region 70. An end of the common electrode 23A isdisposed on a periphery of the display region 70 and connected with aperipheral common electric potential line 50 that provides a commonelectric potential Vcom.

A cross-sectional structure of the connecting portion is shown in FIG.2. The peripheral common electric potential line 50 is formed of a layersame as a layer forming a display signal line 18 and is made of metalincluding aluminum or aluminum alloy or the like. The peripheral commonelectric potential line 50 is formed on an interlayer insulation film16. The common electrode 23A is connected with the peripheral commonelectric potential line 50 through a contact hole CH7 that is formed ina planarization film 20 and the insulation film 22 formed on theperipheral common electric potential line 50. The peripheral commonelectric potential line 50 is connected with a terminal (not shown) on aTFT substrate 10. The common electric potential Vcom is supplied from anIC or the like outside the TFT substrate 10 through the terminal.

The liquid crystal display device according to the embodiment isprovided with neither the auxiliary common electrode line 15 nor the padelectrode 19, which is provided in the conventional liquid crystaldisplay device. As a result, the aperture ratio of the pixel isimproved. Also the common electric potential Vcom is sufficientlysupplied to the common electrode 23A through a low resistance, since thecommon electrode 23A extends over all the pixels in the display region70 and its end is connected with the peripheral common electricpotential line 50.

The peripheral common electric potential line 50 is disposed on theperiphery of the display region 70 along a side of the rectangulardisplay region 70 in a first layout shown in FIG. 3. In order to supplythe common electric potential Vcom to the common electrode 23A througheven lower resistance, it is preferable that the peripheral commonelectric potential line 50 is disposed along each of two sides of thedisplay region 70 facing each other and that the peripheral commonelectric potential line 50 on each side is connected with each end ofthe common electrode 23A, respectively, as in a second layout shown inFIG. 4. In this case, the peripheral common electric potential line 50may be disposed along each of two adjacent sides of the display region70, as in a third layout shown in FIG. 5.

In order to supply the common electric potential Vcom to the commonelectrode 23A through further lower resistance, it is preferable thatthe peripheral common electric potential line 50 is disposed along eachof three sides of the display region 70 and that the peripheral commonelectric potential line 50 on each side is connected with each end ofthe common electrode 23A, as in a fourth layout shown in FIG. 6. Or itis preferable that the peripheral common electric potential line 50 isdisposed along each of four sides of the display region 70 and that theperipheral common electric potential line 50 on each side is connectedwith each end of the common electrode 23A, as in a fifth layout shown inFIG. 7.

However, with the fifth layout shown in FIG. 7, in which the displayregion 70 is surrounded by the peripheral common electric potential line50, it is necessary that a gate line 14 and the display signal line 18are drawn out across the peripheral common electric potential line 50.That is required in order to connect each of the gate line 14 and thedisplay signal line 18 with a corresponding signal source, respectively.

When the peripheral common electric potential line 50 and the displaysignal line 18 are formed of the same layer, it is necessary that eitherthe layer forming the peripheral common electric potential line 50 orthe layer forming the display signal line 18 is partially modified toform a bridge at an intersection of the peripheral common electricpotential line 50 and the display signal line 18 in order to avoid ashort circuit, as shown in a portion surrounded by a dashed line in FIG.7. For example, the display signal line 18 is modified into the samelayer as the gate line 14 at the intersection. The gate line 14 crossesthe peripheral common electric potential line 50 without causing a shortcircuit, because it is formed of the layer different from the layerforming the peripheral common electric potential line 50.

The bridge and the crossing as described above can be avoided bydisposing circuits serving as the signal sources in a region surroundedby the peripheral common electric potential line 50, as shown in FIG. 8.That is, a display signal line control circuit 61 that provides thedisplay signal line 18 with the display signal and a gate line controlcircuit 62 that provides the gate line 14 with the gate signal aredisposed in a region between the display region 70 and the peripheralcommon electric potential line 50.

A liquid crystal display device according to a second embodiment of thisinvention will be explained referring to the drawings. FIG. 9 is a planview showing a portion of a display region in the liquid crystal displaydevice. FIG. 10 is a cross-sectional view showing a section X2-X2 inFIG. 9. FIG. 11 is a cross-sectional view showing a section Y1-Y1 inFIG. 9. Although a large number of pixels are disposed in a matrix formin the display region in the actual liquid crystal display device, onlythree pixels are shown in the plan view.

A relationship between vertical locations of the pixel electrode 21 andthe common electrode 23A in the liquid crystal display device accordingto the first embodiment is reversed in the liquid crystal display deviceaccording to the second embodiment. A common electrode 23B is formed ofthe first layer transparent electrode and a pixel electrode 21B isformed of the second layer transparent electrode above it interposingthe insulation film 22 between them. The pixel electrode 21B in an upperlayer is provided with a plurality of slits S.

With the pixels structured as described above, it is possible to obtaina liquid crystal display device having a wide viewing angle bygenerating lateral electric field between the pixel electrode 21B andthe common electrode 23B and controlling the alignment direction of theliquid crystal molecules.

The pixel electrodes 21B are separated from each other and each of thepixel electrodes 21Bis connected with a source electrode 17 of a TFT 1in the same pixel. The common electrode 23B extends over all the pixelsin the display region 70 as in the liquid crystal display deviceaccording to the first embodiment. An end of the common electrode 23B isdisposed on a periphery of the display region 70 and connected with aperipheral common electric potential line 50 that provides a commonelectric potential Vcom.

A cross-sectional structure of the connecting portion is shown in FIG.10. The peripheral common electric potential line 50 is formed of thesame layer as a display signal line 18 and is made of metal includingaluminum or aluminum alloy or the like. The peripheral common electricpotential line 50 is formed on an interlayer insulation film 16. Thecommon electrode 23B is connected with the peripheral common electricpotential line 50 through a contact hole CH8 that is formed in aplanarization film 20 and the insulation film 22 formed on theperipheral common electric potential line 50. The peripheral commonelectric potential line 50 is connected with a terminal (not shown) on aTFT substrate 10. The common electric potential Vcom is supplied from anIC or the like outside a TFT substrate 10 through the terminal.

Other structures are generally the same as those in the liquid crystaldisplay device according to the first embodiment. That is, the layoutsshown in FIG. 3 through FIG. 8 can be applied to a layout of theperipheral common electric potential line 50 and the common electrode23B to obtain the same effects.

A liquid crystal display device according to a third embodiment of thisinvention will be explained referring to the drawings. The TFT 1 in thepixel in the liquid crystal display device according to the first andsecond embodiments is a polysilicon TFT that has an active layer made ofpolysilicon. Instead, an amorphous silicon TFT 1 a (hereafter referredto as aSi-TFT 1 a) that has an active layer made of amorphous silicon isused in the liquid crystal display device according to the thirdembodiment.

FIG. 12 is a plan view showing a portion of a display region in theliquid crystal display device. FIG. 13 is a cross-sectional view showinga section X3-X3 in FIG. 12. FIG. 14 is a cross-sectional view showing asection Y2-Y2 in FIG. 12. Although a large number of pixels are disposedin a matrix form in the display region in the actual liquid crystaldisplay device, only three pixels are shown in the plan view.

A gate line 114 of the aSi-TFT 1 a is formed on a TFT substrate 100. Thegate line 114 is formed of chromium, molybdenum or the like. A commonelectrode 123B extending over a plurality of pixels is formed in a shapeof stripes in regions except for the gate line 114. The common electrode123B is made of a first layer transparent electrode such as ITO. A gateinsulation film 101 is formed to cover the gate line 114 and the commonelectrode 123B. An amorphous silicon layer 102 is formed on the gateinsulation film 101 to cover the gate line 114. And a display signalline 118 (drain electrode) and a source electrode 103 are formed incontact with the amorphous silicon layer 102.

An interlayer insulation film 104 is formed over the entire surface andthe interlayer insulation film 104 on the source electrode 103 isselectively etched to form a contact hole CH12. There is formed a pixelelectrode 121B that is connected with the source electrode 103 throughthe contact hole CH12. The pixel electrode 121B is made of a secondlayer transparent electrode such as ITO and has a plurality of slits S.The pixel electrode 121B is formed above the common electrode 123B,interposing the gate insulation film 101 and the interlayer insulationfilm 104 between them.

With the pixels using the aSi-TFT 1 a and structured as described above,it is possible to obtain a liquid crystal display device having a wideviewing angle by generating lateral electric field between the pixelelectrode 121B and the common electrode 123B and controlling thealignment direction of the liquid crystal molecules.

An end of the common electrode 123B is disposed on a periphery of thedisplay region 70 and connected with a peripheral common electricpotential line 150 that provides a common electric potential Vcom. Across-sectional structure of the connecting portion is shown in FIG. 13.The peripheral common electric potential line 150 is formed of the samelayer as a display signal line 118 and is made of metal includingaluminum or aluminum alloy or the like. The peripheral common electricpotential line 150 is formed on the gate insulation film 101. The commonelectrode 123B is connected with the peripheral common electricpotential line 150 through a connection wiring 119 that is made of thesecond layer transparent electrode and extending through a contact holeCH13 formed in the gate insulation film 101 and the interlayerinsulation film 104 above the common electrode 123B and a contact holeCH14 formed in the interlayer insulation film 104 above the peripheralcommon electric potential line 150.

The peripheral common electric potential line 150 is connected with aterminal (not shown) on the TFT substrate 100. The common electricpotential Vcom is supplied from an IC or the like outside the TFTsubstrate 100 through the terminal.

Other features such as that the counter substrate is disposed so as toface the TFT substrate 100 and that the liquid crystal is sealed-inbetween the TFT substrate 100 and the counter substrate are the same asin the first and second embodiments, and detailed explanations areomitted.

Neither the auxiliary common electrode line 15 nor the pad electrode 19is provided in the liquid crystal display device according to the thirdembodiment, as in the liquid crystal display devices according to thefirst and second embodiments. As a result, the aperture ratio of thepixel is improved. Also the common electric potential Vcom issufficiently supplied to the common electrode 123B through a lowresistance, since the common electrode 123B extends over all the pixelsin the display region 70 and its end is connected with the peripheralcommon electric potential line 150. Also, the layouts shown in FIG. 3through FIG. 8 can be applied to a layout of the peripheral commonelectric potential line 150 and the common electrode 123B to obtain thesame effects.

A liquid crystal display device according to a fourth embodiment of thisinvention will be explained referring to the drawings. FIG. 15 is a planview showing a portion of a display region in the liquid crystal displaydevice. FIG. 16 is a cross-sectional view showing a section X4-X4 inFIG. 15. FIG. 16 is a cross-sectional view showing a section Y3-Y3 inFIG. 15. Although a large number of pixels are disposed in a matrix formin the display region in the actual liquid crystal display device, onlythree pixels are shown in the plan view.

A relationship between vertical locations of the pixel electrode 121Band the common electrode 123B in the liquid crystal display deviceaccording to the third embodiment is reversed in the liquid crystaldisplay device according to the fourth embodiment. A pixel electrode121A is formed of a first layer transparent electrode and a commonelectrode 123A is formed of a second layer transparent electrode aboveit interposing a gate insulation film 101 and an interlayer insulationfilm 104 between them in the liquid crystal display device according tothe fourth embodiment. The common electrode 123A in an upper layer isprovided with a plurality of slits S.

An end of the common electrode 123A is disposed on a periphery of thedisplay region 70 and connected with a peripheral common electricpotential line 150 that provides a common electric potential Vcom. Across-sectional structure of the connecting portion is shown in FIG. 16.The peripheral common electric potential line 150 is formed of the samelayer as a display signal line 118 and is made of metal includingaluminum or aluminum alloy or the like. The peripheral common electricpotential line 150 is formed on the gate insulation film 101. The commonelectrode 123A is connected with the peripheral common electricpotential line 150 through a contact hole CH15 formed in the interlayerinsulation film 104 above the peripheral common electric potential line150. Other structures are the same as those in the liquid crystaldisplay device according to the third embodiment.

Note that the slits S may extend over a plurality of pixels although theslits S in the common electrode 23A or 123A are formed within a singlepixel in the liquid crystal display devices according to the firstthrough fourth embodiments. Also, the pixel electrodes 21B and 121B mayhave a comb-shaped slit S that is open at one end.

With the liquid crystal display devices according to the embodiments ofthis invention, the auxiliary common electrode line in the displayregion can be removed to improve the aperture ratio of the pixel, sincethe common electrode is provided with the common electric potentialthrough the peripheral common electric potential line disposed on theperiphery of the display region. In addition, the common electrode canbe sufficiently provided with the common electric potential through thelow resistance, because the common electrode is disposed to extend overthe plurality of pixels and connected with the peripheral commonelectric potential line.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The application is claimed as follows:
 1. A display device comprising: asubstrate; a transparent electrode; a plurality of pixels arranged in amatrix in a display region on the substrate, each of the pixels having apixel electrode overlapping the transparent electrode; a common linearranged between the substrate and the transparent electrode, the commonline being a metal line; a layer interposed between the pixel electrodeand the transparent electrode; and a wiring having a first portion, asecond portion, and a third portion, wherein the second portion isarranged between the common line and the substrate and intersects withthe common line in a planer view, wherein the second portion iselectrically connected to the first portion through a second contacthole, wherein the third portion is electrically connected to the secondportion through a third contact hole, wherein the common line iselectrically connected to the transparent electrode through a firstcontact hole, and wherein the common line is arranged along four sidesof the display portion in a planer view.
 2. The display device accordingto claim 1, wherein the third portion of the wiring comprises a samelayer as the first portion.
 3. The display device according to claim 1,wherein the third portion of the wiring is surrounded by the commonline, and a voltage is applied to the wiring line.
 4. The display deviceaccording to claim 1, wherein the common line has four sides eacharranged along each of the four sides of the display portion, thetransparent electrode is electrically connected to the four sides of thecommon line through a plurality of the first contacts.
 5. The displaydevice according to claim 1, further comprising: a plurality of thinfilm transistors in the pixels in the display portion; a plurality ofgate lines electrically connected to the thin film transistors; and agate line control circuit configured to provide a gate signal to each ofthe gate lines.
 6. The display device according to claim 1, furthercomprising: a plurality of thin film transistors in the pixels in thedisplay portion; a plurality of signal lines electrically connected tothe thin film transistors; and a plurality of gate lines electricallyconnected to the thin film transistors; wherein the first portion andthe third portion of the wiring comprise a same layer as the singlelines, and wherein the second portion of the wiring comprises a samelayer as the gate lines.
 7. The display device according to claim 1,wherein the common line and the first contact are disposed outside thedisplay portion.
 8. A display device comprising: a substrate acomprising: an insulating surface; a plurality of pixels arranged in amatrix in a display portion on the insulating surface, each of thepixels including a pixel electrode; a transparent electrode thatoverlaps the pixel electrodes; a layer interposed between the pixelelectrodes and the transparent electrode; and a common line that isdisposed between the insulating surface of the substrate and the layerand that is connected to the transparent electrode through a firstcontact hole, the common line being a metal line; a wiring thatintersects the common line in planar view and that is applied with apredetermined voltage, the wiring including: a first portion; a secondportion that is arranged farther apart from the transparent electrodethan the first portion; and a third portion, wherein the first portionis electrically connected to the second portion through a second contacthole, the third portion is electrically connected to the second portionthrough a third contact hole, the common line and the first contact holeare disposed outside the display portion, and the common line isarranged along four sides of the display portion in planar view.
 9. Thedisplay device according to claim 8, wherein the third portion of thewiring comprises at a same layer as the first portion.
 10. The displaydevice according to claim 8, wherein the common line is disposed betweenthe common electrode and the insulating surface of the substrate. 11.The display device according to claim 8, wherein: the common line hasfour sides each arranged along each of the four sides of the displayportion, and the transparent electrode is electrically connected to thefour sides of the common line through a plurality of the first contactholes.
 12. The display device according to claim 8, further comprising:a plurality of thin film transistors in the pixels in the displayportion; a plurality of gate lines electrically connected to the thinfilm transistors; and a gate line control circuit that provides a gatesignal to each of the gate lines.
 13. The display device according toclaim 8, further comprising: a plurality of thin film transistors in thepixels in the display portion; a plurality of signal lines electricallyconnected to the thin film transistors; and a plurality of gate lineselectrically connected to the thin film transistors; wherein the firstportion and the third portion of the wiring comprise a same layer as thesingle lines, and the second portion of the wiring comprises a samelayer as the gate lines.